fix: recover mcp server port conflicts

[lynnswap]

Purpose

Fix CodexReviewMonitor startup recovery when the MCP HTTP endpoint port is already occupied by a stale process.

Changes

• Classify MCP HTTP bind failures as addressInUse instead of surfacing the raw NIO error.
• Preflight the MCP bind before launching codex app-server, then start the real MCP listener only after the app-server backend is ready.
• Add best-effort port owner diagnostics without exposing full process argv.
• Keep the sidebar in an unavailable server-state presentation for starting, stopped, and failed states.
• Cover port conflict startup, owner diagnostics, bind classification, and sidebar unavailable states in tests.

Testing

• codex-review on uncommitted changes: passed with no findings
• swift test --build-system swiftbuild --no-parallel
• xcodebuild test -project Tools/ReviewMonitor/CodexReviewMonitor.xcodeproj -scheme CodexReviewMonitor -destination 'platform=macOS,arch=arm64' CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO